Field
The present disclosure relates to tires for passenger vehicles, and notably the beads of these tires.
Description of Related Art
Reducing the emissions of greenhouse gases in the field of transport is one of the major challenges facing vehicle manufacturers today. A great deal of progress has been made through tires, by lowering the rolling resistance, because this has a direct impact on vehicle fuel consumption. Notable progress has been achieved and the great success of the Energy™ Saver tire recently marketed by Michelin for example bears witness to this. The technology employed allows around 0.2 l of fuel to be saved per 100 km in mixed cycle, representing a reduction of almost 4 g of CO2 per km. Over the life of a vehicle, that corresponds to approximately one tonne of CO2 that is not released into the atmosphere.
Bearing in mind the predictable increase in the price of crude oil and the ever increasing ecological awareness of consumers, it is nonetheless necessary to continue the battle to reduce the rolling resistance of tires.
The assembly formed by the bead and the radially inner part of the sidewall of a tire is one of the tire components of which the structure has a very marked impact on the rolling resistance of the tire. It has numerous roles: it absorbs the tension in the carcass reinforcement and transmits the loads applied to the tire from the sidewall to the rim. It therefore, from the rim, guides the crown of the tire. Its influence on the roadholding of the tire is considerable, especially when the tire is highly loaded. All of these functions are usually performed by the combination of a reinforcement (comprising the bead wire and the turn-up of the carcass reinforcement about this bead wire) and of a “filler” made of rubber composition. The compromise between the stiffness to be achieved, particularly for guiding the crown, and the expected endurance generally means that a certain path of the carcass reinforcement is planned and use is made of a filler that is bulky (tall and/or thick) and rigid. The downside of this geometry is significant hysteresis losses, particular in the filler. The stiffening action of the filler is applied especially in the region remote from the bead and therefore entails a filler that is even bulkier and, therefore, even greater hysteresis losses.
While searching for a very low rolling resistance tire for passenger vehicles, the applicant company has proposed a tire in which the volume of the filler has been reduced as far as possible and in which the stiffening function is provided by a reinforcement that has very low hysteresis. Such as tire is disclosed in document WO 2011/067211.
That tire, although it allows an excellent compromise between rolling resistance and cornering stiffness, has not lived up to expectations in terms of endurance.